Impactors for breakage of materials are known in the art. Such apparatus includes a rotating chamber arranged to rapidly rotate about an axis. Feed materials such as rock, gravel, mineral ores and the like are passed into the rotor chamber via an inlet and contact a distributor plate located on one side of the chamber opposite to the feed material inlet. The materials slide across the distributor plate and are ejected sideways to impact against the surrounding walls of the impactor, and are thereby attritioned. The rotor chamber can become blocked when too much feed or feed containing large particles chokes the chamber, necessitating stopping of the apparatus. Due to the nature of the feed materials and the duty required of the apparatus, the distribution plate surface is normally made of a high strength alloy metal and this is usually an expensive item. In use the distribution plates are subjected to significant and uneven wear.